The present invention relates to a connector for coupling optical fibers to a light emitter or light-receiver, comprising an optical connection device between optical fibers and said emitter or receiver.
Hereinafter, a bundle of fibers is to be understood to mean an optical light conductor comprising either a single optical fiber or a plurality of fibers which are arranged one adjacent the other in the longitudinal direction.
Nowadays, communication systems are being developed in which optical fibers are used as conductors for light waves modulated by the information to be transmitted. These fibers are thus utilized for long distance in the same manner as electrical conductors. In such systems use can be made of visible and invisible light.
The communication networks used comprise bundle-to-bundle connections and connections between fiber bundles and devices for either injecting light energy into the network or detecting light energy emitted from the network. For the designed and developed systems to be operational, it is necessary that their maintenance can be readily performed and that faulty elements of the network can be readily replaced. This must be the case, for example, for the light emitters and the light receivers. Therefore, connection devices should be available to the user for connecting the fiber bundle to the emitter or receiver, and these devices should consist of two parts, one part accommodating the emitter or the receiver, while the other part is integral with the fiber bundle, the two parts being connected one into the other by way of a locking system which keeps one of the parts in position relative to the other part.
The present state of the art, already knows devices of this kind, whose construction is similar to that of connectors for electrical cables with a co-axial conductor. A device of this kind is described in U.S. Pat. No. 3,948,582. This connector is constructed to provide direct connection of an opto-electronic emitter or receiver to a fiber bundle. The construction of this connector includes facilities to ensure precise positioning of said element, in the axial as well as in the transverse direction, relative to the entrance face of the fiber bundle and its axis in order to achieve optimum coupling from an energy point of view.
In spite of the steps taken, the efficiency of the coupling obtained is always comparatively low, notably in the case where the emitter or the receiver has an emission or reception surface which is substantially smaller than the sectional area of the end of the fiber bundle. It is known that the acceptance angle .alpha. is one of the characteristic properties of optical fibers. Each ray in the fiber travels at which an angle with the optical axis of the fiber which exceeds half .alpha. traverses the lateral surface of the fiber core instead of being reflected thereby, so that it does not contribute to the transport of light energy along the fiber. Consequently, if the surface area of the emitter is much smaller than the entrance face of the fiber bundle, in the case of emission, a major part of the luminous energy emitted is not utilized, notably the energy which is emitted at angles of incidence in excess of half the angle of acceptance .alpha., this part being larger as the angle .alpha. is smaller, while, moreover, the fibers at the periphery of the bundles are apt not to transmit any energy at all. The same is applicable to reception, notably if the receiver has dimensions which are smaller than the sectional area of the end of the bundle; a quantity of light energy transported in the bundle is then not received by the receiver, not even if said receiver is placed in contact with the end section of the bundle.
These drawbacks are mitigated in accordance with the present invention where an optical device is introduced between the end of the fiber bundle and the emitter or receiver. The optical device introduced has dimensions and properties such that it optically connects the surface of the emitter or the receiver to the entrance section of the fiber bundle, the diameter of the image of said surface, produced by the optical system, being substantially equal to the diameter of the fiber bundle, the image aperture angle being at least equal to half the acceptance angle of the fiber bundle. This optical device is described in Ser. No. 748,559, filed on Dec. 8, 1976, by the assignee of the present application, U.S. Pat. No. 4,102,559.
As a result, the invention enables one to efficiently inject light energy from an emitter into a fiber bundle, where the fiber bundle has a small acceptance angle and a large aperture, and where the emitter has a surface which is much smaller than the aperature of the fiber bundle.
The introduction of an optical device of this kind requires a high precision in the axial and transverse directions for the positions occupied by the end of the fiber bundle and the emitter or receiver. Any lack of precision has an adverse effect on the optical connection between them, especially because of the essential enlargement of the optical device and hence has an adverse effect on the quality of the light coupling between the fiber bundle and the emitter or receiver.
An object of the invention is to satisfy these precision requirements. To this end, a connector for connecting an optical fiber bundle to a light emitter or light receiver, according to the invention comprises first and a second connection elements which can be coupled and locked one into the other. The two connection elements each comprise two cylindrical envelopes on the outer face of which are arranged coupling and locking members of the type known for connectors for electrical coaxial cables. The first connection element also comprises a part for mechanically locking the fiber bundle and for holding and supporting said fiber bundle, said mechanical part being integral with the envelope. In the second element there is further provided an optical assembly comprising an emitter or receiver and an optical image forming device, the axis of which is aligned with the axis of said emitter or receiver. This assembly is supported, guided, and held by means which are integral with the envelope. The means for supporting, guiding and holding, inside the two connection elements are arranged so that they accurately position, in the axial as well as in the transverse direction, the end of the fiber bundle and either the emitter or the receiver with respect to each other in the coupled condition. The end of the fiber bundle and the face of the emitter or the receiver are optically connected by the optical device.
The optical device included in a preferred embodiment of this connector is as disclosed in the aforesaid U.S. Pat. No. 4,102,559.
Hereinafter, a preferred embodiment of a connector according to the invention will be described with reference to the accompanying drawing.